At present, there are a number of instruments designed to measure liquid and gas yields. But these instruments are usually very specialized, requiring a level of calibration that is often difficult to attain, and more importantly demanding the presence of a supporting element for the probe or sensor extending into the fluid. For this reason, an opening in the wall of the conduit must be made, and different methods must be used to ensure air and watertightness, under pressure conditions which may exceed 100 bar, often with inflammable or chemically aggressive, and hence dangerous, gases. In addition, many of these instruments for measuring yield are costly, thus limiting their usefulness in the field.
In addition, the technician who wishes to know the amount of global consumption in a linked consumer network sharing a pressure reduction station is often reduced, these days, to listening "by ear" to the sound emitted by the pressure reducing valve in order to estimate the circulating gas yield. Since the intensity of the sound increases with the yield, this operation depends entirely on the sensitivity of the technician's hearing.
Such an evaluation is even more subjective in that the overall sound varies as a function of the pressure upstream of the pressure reducing valve compared to the pressure downstream of the valve, as a function of the temperature and nature of the fluid in circulation, and also as a function of the geometry of the pressure reducing valve and the conduits connected to it.
This last point is particularly important, since many manufacturers have recently come out with "silent" pressure reducing valves which disperse jets of fluid, thereby altering the resonance levels and the emission range of the sounds involved. Under such conditions, evaluating the yield of the product becomes a matter of blind chance.